Foundation void former unit

ABSTRACT

A void former unit ( 10 ) for use in a concrete foundation ( 25 ) includes a plurality of tyres ( 12 ) located side-by-side. The void former can have a retention element in the form of tyre tread or conveyor belt ( 16 ) located around the perimeter of the plurality of tyres. Typically, each tyre has an in-use upper side wall removed therefrom, thus enabling a fill material ( 36 ) to be located within each tyre, and between each tyre and the retention element, and in any voids between the tyres in the unit The improvement comprises arranging a capping element ( 80 ) on the unit and/or in-filling the unit with fill material ( 74,78 ) formed from tyre or conveyor belt material. The unit can be used in a concrete foundation by arranging one or more of the void former units on the ground and in-filling the units with the fill material and/or covering the units with the capping element prior to concrete pouring.

FIELD OF THE INVENTION

The present invention relates to an improved void former unit for use in concrete foundations.

BACKGROUND OF THE INVENTION

Void formers are used to minimise the cost of forming concrete foundations, especially concrete slabs. The use of void formers enables less concrete to be used in forming the slab, whilst reinforcing beams can be defined between adjacent void formers to increase slab strength.

Various void formers are known in the art, including those shown in AU584769, AU585743, AU591816, AU30129/92, AU74322/91, AU37039/89, U.S. Pat. No. 3,109,217, U.S. Pat. No. 3,148,444 and U.S. Pat. No. 4,799,348.

AU710541 discloses the use of vehicle tyres as void formers. The tyres are laid side-by-side to provide a base for a concrete raft slab, and are then overlaid with a mesh which supports a waterproof membrane. Edge and internal beams can also be defined around the tyres, by using a shaped water-impermeable sheet material along the edge of a row of tyres. However, construction of the base must be performed in situ, and the steps of overlaying the tyres with a mesh and then a waterproof membrane, and providing sheet material to define the edge and internal beams, is a cumbersome and time consuming exercise.

The present applicant in AU97131/01 has defined a void former for use in a concrete foundation formed from a plurality of tyres and having a retention element extending therearound to define the void former. The present invention relates to an improved void former.

SUMMARY OF THE PRESENT INVENTION

In a first aspect, the present invention provides a unit for use as a void former in a concrete foundation, the unit including a plurality of tyres located side-by-side, side, wherein a continuous capping element is located on top of the unit in use.

Advantageously, the capping element can define a platform on the void former in use which can support a human user, reinforcing mesh, or pipe work or ducting for utilities and services such as plumbing, gas pipes, electrical conduits, telecommunications conduits etc. Preferably the capping element is fastened to the unit to provide extra stability and so that eg. the unit may be portable. The capping element may be fastened to the unit off-site or on site.

Preferably the capping element is formed from roll-formed sheet material to aid in its structural integrity and strength. In this regard, the roll-formed sheet material is typically roll-formed steel because of its abundance and relatively low cost. Optionally the steel is galvanised or coated to minimise corrosion of the capping element within a concrete slab. Typically the roll-formed sheet is also corrugated to further enhance its structural integrity and strength. The capping element can also be formed from roll-formed sheet material such as roof-sheeting, condeck etc. Such sheet materials have high structural integrity and can be walked on etc.

In a second aspect the present invention provides a unit for use as a void former in a concrete foundation, the unit including a plurality of tyres located side-by-side, wherein a fill material formed from tyre or conveyor belt material is located within and/or between each tyre in use.

By in-filling with tyre or conveyor belt material the overall structural integrity of the void former can be enhanced. The in-filling with tyre or conveyor belt material (especially used tyre or conveyor belt material) is also advantageous environmentally, as off-cuts, scrap etc. of tyre and conveyor belts can be used as the fill material, so that an increased use of an otherwise difficult to dispose of waste can be made.

The tyre or conveyor belt material may also be located in any voids between each tyre and a retention element that extends around a perimeter of the plurality of tyres in use.

Preferably the fill material is employed as tyre sidewalls, coiled tyre tread or tyre conveyor belt, or particulate or granular tyre/conveyor belt material. Various combinations of these can also be used as fill material both within tyres and outside and between tyres.

Preferably, the retention element is one or more lengths of tyre tread or conveyor belt (e.g. mining conveyor belt), typically continuous lengths. Tyre tread and conveyor belt are very strong and provide a structurally stable, inert and corrosion resistant retaining wall for the unit, and allow for ready in-filling of the unit. They are also freely available, especially in used quantities.

Preferably, each of the plurality of tyres has an in-use upper sidewall removed therefrom. This allows for easy in-filling, and for compacting if necessary, of the units with fill material. The use of fill material enhances the strength and support function of the unit in use in a concrete foundation, especially in a monolithic raft slab. This contrasts with the arrangement of AU710541 where no such support function is provided, and the void formers can collapse if walked on.

Other fill materials can be located within each of the plurality of tyres, and between each tyre and the retention element, and in any voids between the tyres in the unit. Suitable fill materials include sand (such as builder's sand), aggregate, crushed cobble stone, etc. These fill materials, may also be mixed with particulate or granular forms of tyre or conveyor belt.

Preferably in the unit each tyre is fixed to each adjacent tyre. It is also preferred that each tyre is fixed at one fixing point at least to the retention element. Preferably, each tyre is fixed using screwing, bolting, pinning and/or adhesive.

Preferably, the retention element is located at the perimeter of the plurality of tyres in a manner such that, when located on ground in use, an undercut with respect to the outermost periphery of the unit is defined between the outside of the element and the ground. Preferably the retention element has, or is sufficiently flexible to define, a transverse curvature that can match the curvature of an outer lateral face of each of the plurality of tyres to thereby define the undercut.

Typically, used or discarded tyres, tyre treads and conveyor belts are employed in the unit, and also as fill. Tyres from any vehicle, including automobiles, trucks, tractors etc can be employed.

In a third aspect, the present invention provides a concrete foundation including one or more units as defined in the first and second aspects of the invention. Preferably, the foundation is a monolithic raft slab.

Preferably, prior to forming the slab, a reinforcing mesh for the slab is located on top of the one or more units. Preferably, prior to locating the reinforcing mesh, the capping element is located on top of each unit.

Preferably, the foundation includes a plurality of units that are positioned to define a plurality of channels therebetween such that, when concrete is poured into those channels, beams are defined which project downwardly in the foundation in use.

Preferably, each beam is keyed into the undercut between the retention element and the ground.

In a fourth aspect, the present invention provides a method for preparing a concrete foundation on ground, including the steps of:

-   -   (i) arranging on the ground one or more units as defined in the         first aspect, absent the capping element;     -   (ii) in-filling the unit(s) with a fill material; and     -   (iii) covering each unit with a respective capping element.

Alternatively, the unit(s) can be prepared off-site by in-filling with fill material and/or capping each unit. The pre-prepared units can then be arranged in a predetermined formation prior to forming the concrete foundation.

Preferably the fill material is located and is as defined for the second aspect of the invention.

Preferably after step (iii) concrete is poured over the prepared concrete foundation to cover the one or more units and to fill any spaces therebetween.

Preferably after step (iii), and prior to concrete pouring, a reinforcing mesh is overlaid the one or more units, which is embedded into the concrete after concrete curing.

Preferably in the fourth aspect the capping element is a roll-formed sheet material such as roof-sheeting, condeck etc. which is cut to size and then positioned on each unit prior to overlaying the reinforcing mesh.

Preferably reinforcing is also arranged in one or more channels defined between adjacent units, which reinforcing is also embedded in the concrete after concrete curing.

In a fifth aspect the present invention provides a method of forming a unit as defined in the first aspect, including the steps of:

-   -   arranging the plurality of tyres side-by-side;     -   optionally fastening a retention element at a perimeter of the         plurality of tyres;     -   sizing and then locating a capping element on the unit.

Prior to locating the capping element on the unit, the unit is preferably filled with fill material as defined in the second aspect of the invention. Preferably the locating of the capping element on the unit includes a step of fixing the capping element to the unit using screws, bolts, pins and/or adhesives.

In a sixth aspect the present invention provides a method of forming a unit as defined in the second aspect of the invention, including the steps of:

-   -   arranging the plurality of tyres side-by-side;     -   optionally fastening a retention element at a perimeter of the         plurality of tyres;     -   in-filling the unit with a fill material formed from tyre or         conveyor belt material.

Preferably the method of the sixth aspect optionally includes the step of locating a capping element on the unit in a manner as defined for the fifth aspect of the invention.

In a seventh aspect, the present invention provides a portable unit for use as a void former in a concrete foundation including a plurality of tyres located side-by-side and having, at a perimeter of the plurality of tyres, a retention element extending therearound.

In an eighth aspect, the present invention provides a unit for use as a void former in a concrete foundation including a plurality of tyres located side-by-side and having, at a perimeter of the plurality of tyres, a continuous retention element extending therearound.

Advantageously, in the seventh aspect, portability is provided for, so that the unit can be formed off site and then transported on site for immediate use. Advantageously the retention element can in both the seventh and eighth aspects function to retain the tyres in the unit, and also retain a fill material therein.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example of only, with reference to the accompanying drawings in which:

FIG. 1 shows a plan view of a preferred void former unit with capping arranged thereover in accordance with the present invention;

FIG. 2 shows a cross-sectional side view through the void former unit of FIG. 1 taken on the line 2-2;

FIG. 3 shows a plan cross-sectional view through the void former unit of FIG. 1 taken on the line 3-3 of FIG. 2;

FIG. 4 shows a similar view to FIG. 1;

FIG. 5 is a cross-sectional side view of the void former of FIG. 4, taken on the line 5-5 and showing a different fill material in the void former unit;

FIG. 6 is a cross-sectional plan view through the void former unit of FIG. 4, taken on the line 6-6 of FIG. 5 and again illustrating a different fill material;

FIG. 7 shows a schematic plan view of a concrete foundation incorporating a plurality of such void former units;

FIG. 8 is a sectional side view through one of the units of FIG. 7, (and part of another unit), and taken on the line A-A in FIG. 7;

FIG. 9 is a perspective view of a foundation at an early stage of preparation;

FIG. 10 is a view of the foundation of FIG. 9, from an opposite end thereof, at a further stage of preparation;

FIG. 11 is a side perspective view of the foundation of FIGS. 9 and 10, at a further advanced stage of preparation using a first method according to the invention;

FIG. 12 is a plan perspective view of a preferred, partly in-filled, void former unit in accordance with the present invention;

FIG. 13 is a perspective view of another foundation at an early stage of preparation, employing the void former unit of FIG. 12; and

FIGS. 14 and 15 are similar perspective views of the foundation of FIG. 13 but in increasingly advanced stages of foundation preparation.

MODES FOR CARRYING OUT THE INVENTION

Referring firstly to FIGS. 1 to 6, a void former lo in accordance with the present invention includes a plurality of, in this case four, tyres 12. Each tyre preferably has an in-use upper tyre side wall removed therefrom (as best seen in FIGS. 2 and 5) and has an in-use lower side wall 14 remaining intact. A retention element in the form of one or more lengths of tyre tread 16 or conveyor belt 16 extends around the perimeter of the four tyres as shown, and is attached thereto via a plurality of fastening elements in the form of screws (e.g. Tec Screws), bolts or pins 18 (one such screw/bolt/pin being shown in FIGS. 3 and 5). Alternatively or additionally industrial strength adhesive may be used. In addition, each tyre is attached to each adjacent tyre, at adjacent treads, by screws, bolts or pins 20 (one such screw/bolt/pin being shown in FIGS. 3 and 5).

A continuous but discrete capping in the form of lid or cap 21 is shown positioned on the void former 10, and is typically fastened thereto in use. Such fastening can be achieved using bolts, screws, pins and/or adhesive. The cap 21 is typically a roll-formed steel sheet, optionally coated with a paint or film, or galvanised to prevent corrosion. Typically a plurality of corrugations 22 are rolled into the sheet to enhance its strength, dimensional stability, and load bearing capacity. For example, roof sheeting or condeck can be employed, and cut to the shape as shown in FIGS. 1 and 4.

A variety of fill materials may be located within each tyre 12, the in-filling being enhanced by the removal of tyre upper sidewall (thereby allowing eg. fill compacting etc.). In the embodiment of FIGS. 1 to 3, tyre sidewalls 23 having been removed from discarded tyres, are stacked within each tyre 12 (as best shown in FIG. 2). In the embodiment of FIGS. 4 to 6, coiled tyre tread or conveyor belt tread 24 is positioned within each tyre 12 (as best shown in FIGS. 5 and 6). Granular or particulate fill can be distributed in and amongst the tyre sidewalls and coiled tread/conveyor belt. This granular or particulate fill can include granulated/particulated tyre and conveyor belt material, and/or typical fill materials described below such as sand, aggregate, rock, cobble etc. Coiled and/or granular/particulate tyre/conveyor belt may also be located in the voids V between tyres 12, and between tyres 12 and element 16.

Typically when conveyor belt is employed as the surrounding retention element, only one join is required. When tyre tread is employed, typically two lengths are required to completely surround the four tyres, so that two joins arise. Typically, the retention element is also continuous, in the sense of extending completely around the plurality of tyres. However, discrete lengths can be employed to extend simply between the screws or bolts 18 of adjacent tyres (i.e. each length functioning more as a discrete tying element).

By fixing together adjacent tyres, and having a retention element extending therearound in the manner as described, the void former can be made portable, and thus can be fabricated off site (e.g. in a factory), with the advantages that economy of scale can arise, and modern in-line manufacturing procedures can be employed etc.

FIG. 7 depicts schematically a plurality of void formers 10 used in a concrete foundation 25. As shown particularly in FIG. 3, concrete is poured so as to leave a step 26 around the perimeter thereof, upon which a course of bricks etc. can be laid. The concrete is poured so as to define a monolithic slab 28 which effectively encapsulates the void formers as shown in FIGS. 2 and 3. Concrete also flows into channels 29 defined between adjacent void formers, to define a series of beams as described below.

As also shown in FIG. 7, void formers can also be formed from units 30 comprising two tyres, or from units including fractions of tyres, such as a 1½-tyre unit 32, or a three-tyre unit 34 (that includes two adjacent half tyres).

Referring now to FIG. 8, a cross section through the void former 10 of FIGS. 1 to 6 with the cap 21 located thereon is shown when located within slab 28. As can be seen, each tyre has a fill material 36 located therewithin, such in-filling being readily facilitated by the removal of the tyre upper side wall in each case. The fill material can be tyres/conveyor belt (as described above) and/or fill that is lightly compacted within each void former. Typical compactable fill materials include sand (such as builder's sand or yellow sand), aggregate, granulated rock, crushed rock or cobble, blue metal, etc. Such compactable fill material can also be introduced into the voids V (FIGS. 3 and 6) located between tyres, and between the tyres and the tread or belt 16.

FIG. 8 also shows how reinforcing rods or bars 40 (typically made of steel or other alloy) are arranged in channels 29, typically towards the base of each channel. Outside perimeter bars 42, which are inset from the perimeter of the concrete foundation, are also provided within the slab. The bars 40 help define and strengthen the resultant internal concrete beams 44, and the bars 42 help define and strengthen the resultant external concrete beams 46, both of which extend down from slab 28 after the pouring and curing of concrete.

Reinforcing mesh 48 (typically formed from steel or other alloy) is arranged in an upper part of the slab 28 to reinforce and strengthen the slab once cured. Typically this mesh overlies the caps 21 as shown. However, as shown in FIG. 11, the rods 40, 42 are spaced from underlying ground by lower spacers 50, and the mesh 48 is spaced above the void formers 10 by upper spacers 52, positioned as shown on the void formers absent a cap 21. The edges of the reinforcing mesh can be finished off with a reinforcing bar 54 (FIG. 8) to provide structural integrity to the slab at the edges thereof.

As is known, tyre treads have a curvature in cross section, as depicted in FIGS. 2, 5 and 8. The retention element tyre tread or belt 16 is preferably wrapped around the tyres and either has a similar shape, or sufficient flexibility, such that, when attached to the tyres 12 in each void former, the element maintains this curvature, again as shown in FIGS. 2, 5 and 8. This in turn has the effect of defining an undercut 56 around each of the void formers, and into which concrete can flow when the slab 28 is poured. The undercut has the effect of capturing the void formers within the concrete foundation, thus enhancing the overall structural integrity of the formation. In addition, by locating the bars 40, 42 close to this undercut region within both the internal and external beams, the strength of the beams adjacent to the undercut is enhanced.

Referring now to FIGS. 9, 10 and 11, and initially to FIG. 9, when constructing a concrete foundation, more particularly a concrete slab using void formers in accordance with the present invention, a moisture barrier in the form of sheet 58 (typically a plastic sheet) is laid onto pre-prepared ground, and over and between a surrounding form work 60, defining the perimeter of the concrete foundation. Empty void formers (left hand side of FIG. 9) are then positioned on the sheet 58 in a desired location to define channels 29 therebetween. Fill material 36 (including tyres and conveyor belt) is then introduced into each void former and, if compactable, is lightly compacted (eg with a mechanical compactor or manually), until each of the void formers are compactly filled (FIG. 10).

FIG. 10 also illustrates that differently sized void formers in differing locations can be employed. Some of those void formers (e.g. void formers 62) can simply be defined by tyre tread or conveyor belt formed into a loop and filled with fill material (eg. with no whole tyres being disposed therewithin).

Typically a cap 21 is cut to size and positioned on top of each void former unit. However, in this embodiment the caps 21 are omitted. Reinforcing is then arranged in the concrete foundation, with rods 40 being positioned in each channel 29 (FIG. 11) and spaced above the sheet 58 by spacers 50. Reinforcing mesh 48 is then located and spaced above the void formers 10 by upper spacers 52.

The concrete foundation is now ready to receive a concrete pour in a known manner, to define the concrete foundation 25 of FIG. 7.

Referring now to FIGS. 12 to 15, a void former 70 is depicted. Again, the void former 70 includes four tyres 72, each preferably having an in-use upper side wall removed therefrom, but with the lower side wall remaining intact. In this embodiment, a plurality of tyre sidewalls 74 are stacked within each tyre of the unit. Typically the tyre sidewalls are stacked up to the top of each tyre. The sidewalls increase the structural stability of the tyre whilst also disposing of waste cut tyre sidewalls. Again, tyre tread or conveyor belt 76 extends continuously around the perimeter of the four tyres and is attached to the tyres via a fastening element (eg. bolts, screws etc.).

As a further fill material, and as a means of enhancing void former strength and load bearing capacity, whilst disposing of further tyre or conveyor belt material, coils 78 of either tyre tread or conveyor belt are rolled and positioned within each of the tyres (ie. in the hole 79 defined in the sidewall stack) and between tyres. One such coil only is shown in FIG. 12, but multiple numbers of coil units can be positioned within and between the tyres (eg. in the voids V).

Again, as for void former 10, fill material (including granulated/particulate tyre tread or conveyor belt) can be introduced into the centre of each tyre and between tyres, and also between tyres and the retention element. However, if no fill material is readily available, the void former 70 can be filled with tyre and belt scrap material (side walls, tread, belt off-cuts etc.) and can even function without the use of a fill material.

Referring now to FIG. 13, each unit can have a cap in the form of a continuous but discrete platform 80 positioned thereon. Typically the platform is fastened to the unit with screws. This can be done either on-site, or off-site in a factory and the units then transported on-site. The platform is typically formed from a roll-formed sheet material (e.g. a roofing material such as corrugated steel roofing). Alternatively, material such as condeck (i.e. concrete support decking) can be employed. Even flat sheet material can be used, including masonite; low, medium or high density fibre board etc. Because the void former will ultimately be embedded in a concrete slab, continuous scraps or off-cuts can also be employed as the platform, and even leftover/waste formwork timber material can be employed. The platform can also be employed with or without fill material.

From FIG. 13, it will be seen that each void former 70 has been positioned and levelled (e.g. using a levelling beam 82). Reinforcing rods or bars 83 are then positioned in channels 84 between the void formers. Platforms 80 are cut, positioned and then fastened to each unit. Typically the platforms are cut to have a shape corresponding to that of the void former in plan. The platform can also have holes easily cut therein to support and accommodate any plumbing and electrical conduits 85, as also shown in FIG. 13. Tradesmen can also stand on the platform when fitting these conduits.

Referring to FIG. 14, once each void former has been fitted with its associated platform, reinforcing steel mesh 86 can be positioned on top of all of the void formers. The provision of the platforms 80 makes it easy for a tradesman to walk across the void formers, and the integrity of the void former means that weight is transferred evenly from the platform to the void former and through to the underlying ground without void former collapse, displacement etc.

As shown in FIG. 15, typically the mesh 86 is spaced above the void formers by employing a plurality of spacing elements 88 (as is known). Once the reinforcing steel mesh completely covers the foundation, concrete can be poured into the foundation (typically by being pumped thereover), the concrete filling the channels between the void formers, and covering the void formers by sitting on top of the platforms thereof. The concrete progressively fills up and embeds the steel mesh therein.

A number of advantages can be identified with the void formers and construction methods as defined above:

-   -   The void formers are structurally superior to prior art void         formers, attributable to the use of tyres, and retaining tyre         tread or conveyor belt, both of which are very strong and         durable, having high tensile and reasonable compressive strength         (especially when filled).     -   The void formers when filled eliminate air voids found in         existing void formers, including those disclosed in Australian         Patent 710541, and thus the resultant concrete foundation (slab)         has increased strength.     -   The void formers can be filled with fill excavated from the site         where the concrete foundation is to be laid, thus making use of         that fill and not requiring it to be dumped.     -   The removal of tyre upper side walls also enables the fill         material to be compacted in the void formers in use, thus         increasing their structural integrity.     -   The removal of the tyre upper side wall enables a stack of tyre         side walls to be located in each tyre, and tyre and belt tread         can be coiled and located within and between the tyres in the         void former.     -   Also, granulated tyre or belt material can fill each void         former, disposing further of these waste products.     -   The use of a cap or platform with each void former makes it easy         for users to walk across the foundation, and facilitate for         positioning of reinforcing mesh, plumbing and electrical         conduits etc.     -   The use of the cap or platform also enhances the support offered         by the void formers to spacing elements associated with the         reinforcing steel mesh, which further simplifies the concrete         pouring procedure.

Whilst the invention has been described with reference to a number of preferred embodiments, it should be appreciated that the invention can be embodied in many other forms. 

1. A unit for use as a void former in a concrete foundation, the unit including a plurality of tyres located side-by-side, wherein a continuous capping element is located on top of the unit in use.
 2. A unit as claimed in claim 1 wherein the capping element is fastened to the unit in use.
 3. A unit as claimed in claim 1 or 2 wherein the capping element defines a platform on the void former which in use can support a human user, reinforcing mesh, or utilities pipework and/or ducting.
 4. A unit as claimed in any one of the preceding claims wherein the capping element is a roll-formed sheet material.
 5. A unit as claimed in claim 4 wherein the roll-formed sheet material is roll-formed steel which is optionally galvanised or coated.
 6. A unit as claimed in claim 4 or 5 wherein the roll-formed sheet is corrugated.
 7. A unit for use as a void former in a concrete foundation, the unit including a plurality of tyres located side-by-side, wherein a fill material formed from tyre or conveyor belt material is located within and/or between each tyre in use.
 8. A unit as claimed in claim 7 wherein the tyre or conveyor belt material is located in voids within and between each tyre.
 9. A unit as claimed in claim 7 or 8 wherein the material located within each tyre includes tyre side walls, coiled tyre tread or coiled conveyor belt, and/or particulate tyre/conveyor belt material.
 10. A unit as claimed in claim 7 or 8 wherein the material located outside each tyre in the unit includes coiled tyre tread/conveyor belt and/or particulate tyre/conveyor belt material.
 11. A unit as claimed in any one of claims 7 to 10 wherein a further fill material of sand, aggregate or crushed cobble stone is dispersed through the tyre or conveyor belt fill material.
 12. A unit as claimed in any one of the preceding claims wherein a retention element is provided to extend around a perimeter of the plurality of tyres.
 13. A unit as claimed in claim 12 wherein the retention element extends continuously around the perimeter of the plurality of tyres.
 14. A unit as claimed in claim 12 or 13 wherein the retention element is one or more lengths of tyre tread or conveyor belt.
 15. A unit as claimed in any one of claims 12 to 14 wherein the retention element is located at the perimeter of the plurality of tyres in a manner such that, when located on ground in use, an undercut with respect to the outermost periphery of the unit is defined between the outside of the retention element and the ground.
 16. A unit as claimed in claim 15 wherein the retention element has, or is sufficiently flexible to define, a transverse curvature that can match the curvature of an outer lateral face of each of the plurality of tyres to thereby define the undercut.
 17. A unit as claimed in any one of claims 12 to 16 wherein each tyre in the unit is fixed to each adjacent tyre, and each tyre is fixed at one fixing point at least to the retention element.
 18. A unit as claimed in claim 17 wherein each tyre is fixed using screwing, bolting, pinning and/or adhesive.
 19. A unit as claimed in any one of claims 1 to 6 wherein a fill material is located within each tyre in use.
 20. A unit as claimed in claim 19 wherein the fill material is located in voids within and between each tyre.
 21. A unit as claimed in claim 19 or 20 wherein the fill material includes sand, aggregate or crushed cobble stone.
 22. A unit as claimed in claim 21 wherein the fill material is, alternatively or additionally, tyre or conveyor belt material.
 23. A unit as claimed in claim 22 wherein the fill material located within each tyre includes tyre side walls, coiled tyre tread or coiled conveyor belt, and/or particulate tyre/conveyor belt material.
 24. A unit as claimed in claim 22 or 23 wherein the fill material located outside each tyre in the unit includes coiled tyre tread/conveyor belt, and/or particulate tyre/conveyor belt material.
 25. A unit as claimed in any one of claims 7 to 11 further including a capping element located on top of the unit in use.
 26. A unit as claimed in claim 25 wherein the capping element defines a continuous platform on the void former which is fastened to the unit and in use can support a human user, reinforcing mesh, or utilities pipework and/or ducting.
 27. A unit as claimed in claim 25 or 26 wherein the capping element is a roll-formed sheet material.
 28. A unit as claimed in claim 27 where the roll-formed sheet material is roll-formed steel which is optionally galvanised or coated.
 29. A unit as claimed in claim 27 or 28 wherein the roll-formed sheet is corrugated.
 30. A unit as claimed in any one of the preceding claims wherein each tyre in the unit has an in-use upper sidewall removed therefrom.
 31. A concrete foundation including one or more units as defined in any one of the preceding claims.
 32. A foundation as claimed in claim 31 that is a monolithic raft slab.
 33. A foundation as claimed in claim 32 wherein, prior to forming the slab, a reinforcing mesh for the slab is located on top of the one or more units.
 34. A foundation as claimed in any one of claims 31 to 33 that includes a plurality of units positioned to define a plurality of channels therebetween such that, when concrete is poured into those channels, beams are defined which project downwardly in the foundation in use.
 35. A foundation as claimed in claim 34 wherein each beam is keyed into an undercut defined between the unit and the ground.
 36. A method for preparing a concrete foundation on ground, including the steps of: (i) arranging on the ground one or more units as defined in any one of claims 1 to 6, absent the capping element; (ii) in-filling the unit(s) with a fill material; and (iii) covering each unit with a respective capping element.
 37. A method as claimed in claim 36 wherein the fill material is located and is as defined in any one of claims 19 to
 24. 38. A method as claimed in claim 36 or 37 wherein, after step (iii), concrete is poured over the prepared concrete foundation to cover the one or more units and to fill any spaces therebetween.
 39. A method as claimed in claim 38 wherein, after step (iii), and prior to concrete pouring, a reinforcing mesh is overlaid the one or more units, which is embedded in the concrete after concrete curing.
 40. A method as claimed in claim 38 or 39 wherein reinforcing is arranged in one or more channels defined between adjacent units, which reinforcing is embedded in the concrete after concrete curing.
 41. A method as claimed in any one of the preceding claims 36 to 40 wherein the capping element is a roll-formed sheet material which is cut to size and then positioned on each unit prior to overlaying the reinforcing mesh.
 42. A method of forming a unit as defined in any one of claims 1 to 6 including the steps of: arranging the plurality of tyres side-by-side; sizing and then locating the capping element on the unit.
 43. A method as claimed in claim 42 wherein, after arranging the tyres and prior to locating the capping element, a retention element as defined in any one of claims 12 to 18 is fastened at the perimeter of the plurality of tyres.
 44. A method as claimed in claim 42 or 43 wherein, prior to locating the capping element on the unit, the unit is filled with a fill material as defined in any one of claims 19 to
 24. 45. A method as claimed in any one of claims 42 to 44 wherein the step of locating the capping element on the unit includes a further step of fixing the capping element to the unit using screws, bolts, pins and/or adhesive.
 46. A method of forming a unit as defined in any one of claims 7 to 11 including the steps of: arranging the plurality of tyres side-by-side; in-filling the unit with a fill material formed from tyre or conveyor belt material.
 47. A method as claimed in claim 46 wherein, after arranging the tyres and prior to in-filling the unit with the fill material, a retention element as defined in any one of claims 12 to 18 is fastened at the perimeter of the plurality of tyres.
 48. A method as claimed in claim 46 or 47, further including the step of locating a capping element on the unit in a manner as defined in any one of claims 42 to
 45. 